Theoretical prediction of thermodynamic properties of tritiated beryllium molecules and application to ITER source term

Abstract

By quantum chemistry calculations, we have evaluated the standard enthalpies of formation of some gaseous species of the BeOH chemical system: BeH, BeH2, BeOH, Be(OH)2 for which the values in the referenced thermodynamic databases (NIST-JANAF [1] or COACH [2]) were, due to the lack of experimental data, estimated or reported with a large uncertainty. Comparison between post-HF, DFT approaches and available experimental data allows validation of the ability of an accurate exchange-correlation functional, VSXC, to predict the thermo-chemical properties of the beryllium species of interest. Deviation of enthalpy of formation induced by changes in hydrogen isotopy has been also calculated. From these new theoretically determinated data, we have calculated the chemical speciation in conditions simulating an accident of water ingress in the vacuum vessel of ITER.